One of the building blocks in the evolution of the Third Generation Partnership Project (3GPP) evolved UMTS Terrestrial Radio Access (E-UTRA, sometimes referred to as Long Term Evolution LTE or LTE-Advanced)) system in Release 12 and onward is proximity services (ProSe) which relates to the physical position of the user equipment (UE). ProSe encompasses discovery of one UE by another within its proximity, and this discovery can be based on direct radio signals between these two UEs or on network-side proximity detection at the network side. ProSe also encompasses optimizing the communication path for UEs that are in proximity to one another, which can be realized by the direct communication between UEs or by a local switch within the E-UTRA network (E-UTRAN). A work item has been approved in the 3GPP for this purpose; see document S2-124826 entitled “WID for Proximity Services Specification” (3GPP TSG SA WG2 Meeting 394; New Orleans, US; 12-16 Nov. 2012); and document RP-121698 by Qualcomm, Inc. entitled “Study on LTE Device to Device Proximity Services” (3GPP TSG RAN Meeting #58).
For D2D communications operation, it is envisioned the control of D2D link is shared between the ProSe-enabled UE and the network (namely, the eNodeB or eNB in the case of E-UTRAN) when the ProSe-enabled UEs are served by an E-UTRAN. Document “Direct Communication in 3GPP” by Hakseong KIM of LG (undated, metadata indicates it was created on Oct. 15, 2012) details that the eNB schedules the radio resources for the D2D communication link but the UEs handle the link adaptation by themselves, in order to reduce the control signalling overhead such as frequent channel state reports to E-UTRAN that might otherwise be needed of the network did the link adaptation.
The eNB schedules radio resources via the Physical Downlink Control Channel (PDCCH), or via the ePDCCH. FIG. 1 is reproduced from table 6.8A.1-2 of 3GPP TS 36.211 V11.2.0 “Physical channels and modulation” and shows the formats supported by the ePDCCH. FIG. 2 is reproduced from table 6.8.1-1 of 3GPP TS 36.213 V11.2.0 “Physical layer procedures” and shows the formats supported by the PDCCH.